Open AccessMultidisciplinary Constraints on the Abundance of Diamond and Eclogite in the Cratonic Lithosphere
Author(s) -
Garber Joshua M.,
Maurya Satish,
Hernandez JeanAlexis,
Duncan Megan S.,
Zeng Li,
Zhang Hongluo L.,
Faul Ulrich,
McCammon Catherine,
Montagner JeanPaul,
Moresi Louis,
Romanowicz Barbara A.,
Rudnick Roberta L.,
Stixrude Lars
Publication year - 2018
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2018gc007534
Subject(s) - eclogite , geology , kimberlite , peridotite , xenolith , lithosphere , geothermal gradient , mantle (geology) , craton , petrology , geochemistry , geophysics , seismology , tectonics , subduction
Some seismic models derived from tomographic studies indicate elevated shear‐wave velocities (≥4.7 km/s) around 120–150 km depth in cratonic lithospheric mantle. These velocities are higher than those of cratonic peridotites, even assuming a cold cratonic geotherm (i.e., 35 mW/m 2 surface heat flux) and accounting for compositional heterogeneity in cratonic peridotite xenoliths and the effects of anelasticity. We reviewed various geophysical and petrologic constraints on the nature of cratonic roots (seismic velocities, lithology/mineralogy, electrical conductivity, and gravity) and explored a range of permissible rock and mineral assemblages that can explain the high seismic velocities. These constraints suggest that diamond and eclogite are the most likely high‐ V s candidates to explain the observed velocities, but matching the high shear‐wave velocities requires either a large proportion of eclogite (>50 vol.%) or the presence of up to 3 vol.% diamond, with the exact values depending on peridotite and eclogite compositions and the geotherm. Both of these estimates are higher than predicted by observations made on natural samples from kimberlites. However, a combination of ≤20 vol.% eclogite and ~2 vol.% diamond may account for high shear‐wave velocities, in proportions consistent with multiple geophysical observables, data from natural samples, and within mass balance constraints for global carbon. Our results further show that cratonic thermal structure need not be significantly cooler than determined from xenolith thermobarometry.